Add function and tests for markdown chunks using pygment langs like {.py and {.python etc

src/blacken_docs/__init__.py

@@ -13,10 +13,14 @@
 from black.mode import TargetVersion
 
 
-PYGMENTS_PY_LANGS = frozenset(("python", "py", "sage", "python3", "py3", "numpy"))
+PYGMENTS_PY_LANGS = frozenset(
+    ("python", "py", "sage", "python3", "py3", "numpy", ".py", ".python")
+)
 PYGMENTS_PY_LANGS_RE_FRAGMENT = f"({'|'.join(PYGMENTS_PY_LANGS)})"
 MD_RE = re.compile(
-    r"(?P<before>^(?P<indent> *)```\s*" + PYGMENTS_PY_LANGS_RE_FRAGMENT + r"( .*?)?\n)"
+    r"(?P<before>^(?P<indent> *)```\s*(\{?\s*)?"
+    + PYGMENTS_PY_LANGS_RE_FRAGMENT
+    + r"( .*?)?\n)"
     r"(?P<code>.*?)"
     r"(?P<after>^(?P=indent)```\s*$)",
     re.DOTALL | re.MULTILINE,

tests/test_blacken_docs.py

@@ -944,3 +944,57 @@ def test_format_src_rst_pycon_comment_before_promopt():
         "    # Comment about next line\n"
         "    >>> pass\n"
     )
+
+
+def test_format_src_markdown_pymdown_1():
+    before = dedent(
+        """\
+        ```{.python title='example.py'}
+        f(1,2,3)
+        ```
+        """
+    )
+    after, _ = blacken_docs.format_str(before, BLACK_MODE)
+    assert after == dedent(
+        """\
+        ```{.python title='example.py'}
+        f(1, 2, 3)
+        ```
+        """
+    )
+
+
+def test_format_src_markdown_pymdown_2():
+    before = dedent(
+        """\
+        ```    {.py title='example.py'}
+        f(1,2,3)
+        ```
+        """
+    )
+    after, _ = blacken_docs.format_str(before, BLACK_MODE)
+    assert after == dedent(
+        """\
+        ```    {.py title='example.py'}
+        f(1, 2, 3)
+        ```
+        """
+    )
+
+
+def test_format_src_markdown_pymdown_3():
+    before = dedent(
+        """\
+        ```{    .py .python .extra-class #id linenums="1" title="example.py"}
+        f(1,2,3)
+        ```
+        """
+    )
+    after, _ = blacken_docs.format_str(before, BLACK_MODE)
+    assert after == dedent(
+        """\
+        ```{    .py .python .extra-class #id linenums="1" title="example.py"}
+        f(1, 2, 3)
+        ```
+        """
+    )